The invention relates to a method of storing reduced glutathione for extended periods of time. Normally, when a solution of reduced glutathione is stored, the percentage of biologically active glutathione which is present in solution undergoes a significant reduction over time. This is due to degradation of glutathione in solution. The current invention provides a method of storing reduced glutathione in solution for an extended period of time with little or no change in the concentration of the active ingredient.
Glutathione, a tripeptide containing a free thiol group, is an important antioxidant. In preliminary research, dietary glutathione intake from fruit and raw vegetables has been associated with protection against some forms of cancer. Glutathione has also inhibited cancer in test tube and animal studies. In preliminary research, higher glutathione levels have also been associated with good health in older adults. In fact, glutathione levels appear to show a very strong correlation with life expectancy. The reduced glutathione (G-SH) molecule consists of three amino acidsxe2x80x94glutamic acid, cysteine, and glycinexe2x80x94covalently joined end-to-end. The sulfhydryl group, which gives the molecule its electron-donating character, comes from the cysteine residue. Glutathione is present inside cells mainly in its reduced form.
Studies using intravenous or intramuscular glutathione have found it to be useful for preventing clot formation during operations; reducing the side effects and increasing the efficacy of chemotherapy drugs (particularly cisplatin in women with ovarian cancer); treating Parkinson""s disease; reducing blood pressure in diabetics with high blood pressure; and increasing sperm counts in men with low sperm counts. Whether oral preparations are also effective is unknown at this time. A small study in eight patients with liver cancer using oral glutathione showed modest effects in women but not in men when given in a daily amount of 5,000 mg.
In the healthy cell, the concentration of oxidized glutathione (G-SS-G) is normally less than 10 percent of the total glutathione concentration. The ratio of reduced glutathione to oxidized glutathione appears to be an important indicator of the cell""s health, and of its ability to resist oxidative stress. A reduction of reduced glutathione in a cell can trigger suicide of the cell by a process known as apoptosis.
Reduced glutathione (GSH) works as a potent anti-oxidant in the treatment of Parkinson""s disease. According to research by Dr. David Perlmutter on alterations in glutathione levels, there seems to be both a clinical and neuropathological difference in Parkinson""s disease patients treated with IV glutathione versus control groups. Dr. Perlmutter measured both GSH levels and oxidized glutathione (GSSG) levels in the brains of both Parkinson""s patients and in the brains of patients in control groups. Glutathione levels were reduced approximately 40% and oxidized glutathione was increased approximately 29% in the patients with Parkinson""s disease. This altered GSH/GSSG ratio in the brain may indicate that oxidative stress is a factor in brain cell death in Parkinson""s disease. Therefore, treatment of Parkinson""s disease with pure reduced glutathione may help to delay the progression of the disease.
Treatment of patients with lung diseases such as pulmonary fibrosis and emphysema with reduced glutathione is also useful. Reduced glutathione acts as an antioxidant, preventing oxidants in pollution and cigarette smoke from causing further damage to the lungs.
Unfortunately, reduced glutathione is not stable when subjected to long-term storage. The thiol group on the glutathione undergoes gradual oxidation to a disulfide, as shown: 
This reaction is catalyzed by the presence of molecular oxygen or of certain metal ions, such as Fe+3, but it will proceed in aqueous solution in the absence of catalytic agents. As this reaction proceeds, there is a gradual reduction in the efficacy of the reduced glutathione solution against Parkinson""s. In fact, if greater than 10% of the total glutathione in the reduced glutathione solution has undergone oxidation, the treatment may conceivably increase oxidative stress in the brain, exacerbating Parkinson""s disease.
Thus, there is a long-felt need in the art for a method of storing aqueous solutions of reduced glutathione without allowing oxidation of the glutathione to a disulfide.
The current invention is directed toward extended storage of reduced glutathione in an aqueous medium having a pH of between 5.0 and 8.0, preferably between 6.2 and 7.8. The solution of reduced glutathione has a defined initial concentration. Even in the absence of oxidation catalysts such as molecular oxygen and/or metal ions, the concentration of reduced glutathione frequently undergoes a gradual reduction of between 10% and 15% of the initial concentration per month. It has been unexpectedly found that storing the reduced glutathione solution at a reduced temperature, which is above the freezing point of the solution and below 15xc2x0 C., maintains the rate of reduced glutathione decay at between 0% and 5% of the defined initial concentration per month.
Thus this invention provides a method for extended storage of reduced glutathione by dissolving a predetermined quantity of reduced glutathione in an aqueous medium having a pH of between 5.0 and 8.0 to produce a reduced glutathione solution having a predetermined initial concentration; reducing the temperature of the reduced glutathione solution to a predetermined temperature which is sufficiently low to prevent oxidative dimerization of glutathione without freezing the aqueous medium; and storing the reduced glutathione solution at the predetermined temperature.